Diabetes is a cause of serious myocardial disease related to an increased incidence of coronary artery disease, probably aggravated by cardiac autonomic neuropathy (CAN). In its incipient form, CAN hardly changes the sinus rhythm with an increase in nocturnal heart rate but without an appreciable effect on the indices of variability. In more advanced forms, "CAN+", there are not only changes in the heart rate variability but also in ventricular repolarisation. It is classical to underline the value of the corrected QT interval but this index has little real value. The "QT dispersion", comparing the duration of ventricular repolarisation on the surface leads, is no better a marker from the theoretical point of view. The dynamics of ventricular repolarisation on the other hand seem to be much more indicative of ventricular myocardial disease. They are studied by evaluating the QT-heart rate relationship and its increase distinguishes clearly CAN diabetics from CAN+ diabetics. In addition, in the latter subjects, diurnal physiological increase in the heart rate dependency of the QT interval (QT/RR slope) disappears or even inverse. It is probably this phenomenon which is responsible for the traditionally increased risk of ventricular arrhythmias and particularly sudden death in diabetics with autonomic neuropathy.